Ac68u AP suddenly stopped working

Hi All

I have the following configuration with 2 ac68us
Main router with cable Internet connected via ethernet cable to the other ac68u via ethernet cable. Everything was working fine until this afternoon when the AP router had no intenet access. The Internet led glows fine but I cannot access the net. I tried everything. Resetting both routers. Updating firmware but nothing!!! It's been hardly a month since I have it. The main router connects to the net.

Any suggestions.

Thanks

Sunny